Global grain yields have tripled since 1950 through the use of improved crop varieties
and modern crop management techniques, but elevated CO2 may
put an end to this Green Revolution. In the past 50 years, atmospheric
CO2 has risen from 315 to 392 ppm. If anthropogenic
CO2 production continues to accelerate, atmospheric CO2
may exceed 950 ppm by the end of the century.

Many have claimed that high atmospheric CO2
will increase crop productivity worldwide. High atmospheric CO2
does increase photosynthesis which can result in greater plant growth
and yield, but research from the University of California suggests CO2
fertilization could negatively impact food production.

Protein in all animal life originates from inorganic
nitrogen assimilated by plants and algae. At elevated CO2,
plant nitrate assimilation is inhibited. Many studies have shown a drop
in grain protein content at CO2 levels of only 500 ppm.
At 950 ppm CO2 grain protein content decreases could be large
enough to spur a global protein crisis.

With human population expected to reach 15 billion by 2100, humans will have to turn to alternative
sources of protein. Unfortunately, the decrease in plant protein
content is not limited to grain crops. High atmospheric CO2
also decreases leaf protein in most plant species. This decrease in forage crop protein at elevated CO2 will negatively impact
the animals humans currently consume.

As land plant and mammal protein content declines,
humans in the twenty second century may have to turn to unconventional
sources of protein.

Ocean farming may become a viable alternative to
conventional ranching and agriculture as it does not require arable
land or fresh water and algae protein content is relatively unaffected
by elevated atmospheric CO2. High-energy plankton farms may be the best source of protein for future generations.